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Details, datasheet, quote on part number:PBL3860A/6
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March 1997
Application Note
PBL 3860A/6 Ring Through SLIC
The Ring Through SLIC ( RTS ) application is a method to allow a low voltage ring-signal to be amplified in the SLIC and transferred to the subscriber. There are several advantages with this application compared to a traditional solution. First of all no high voltage ringgenerator is needed. Furthermore, since the ring-signal is connected to the line, in the same way as an ordinary voice signal, no ring relay is required either. The ordinary internal SLIC ring-trip detector is not used in this application. Therefore the ordinary ring-trip network is omitted. With a battery voltage, VBat, of -80V during ringing, a balanced sine wave ring-signal of minimum 40Vrms is guaranteed across a 5REN load at the end of a 100 wire resistance loop.
Transmit Gain The two-wire to four-wire gain between the TIPX - RINGX input and the VTX ground output is calculated as ZT/1000 G2-4 = ZT /1000 +2 ˇ (RF + RP) Receive Gain The four-wire to two-wire gain between the TIPX - RINGX output and the VRX to ground input is calculated in the active state, as: -ZT ZRX ZL ZT/1000 + 2 ˇ (RF + RP) + ZL This stage decreases the amplitude of the signal 39 times and relates it to ground. Due to the fact that we don't want leakage from the line to ground the resistors need to be high impedance, therefore the values are: RDT1, RDR1 = 10k, RDT2, RDR2 = 390k As the RSN input on the SLIC is a current input this pin can be used to mix the signal from the ring-loop and the signal source. The output voltage from the ring-loop is fed to a switch, which in its turn is connected to the RSN pin, by the RRS resistor. In the same way the signal source is connected to this point via the RRG resistor. When the switch is turned on, these resistors acts as voltage to current converters. The resulting current that flows into the RSN input, IS, can be calculated as follows: Vg(t) IS(t) = RRG + RRS ˇ VTR(t)
G4-2 =
ˇ
If RT = 442 k, RF = RP = 40 , VTR/VRX =1 and ZL = 600 this yields RRX=221 k. Balance Network ZRX ZT ZT/100 0+ 2 ˇ (RF +RP) + ZL 2 ˇ (RF + RP) + ZL
Programming of the SLIC
For the programming of the battery feed characteristics and loop detector level, refer to the Telecommunication Circuits Databook. Those parts that are affected in the RTS application will be explained in this application note. Output Impedance The two-wire impedance, ZTR , presented by the SLIC to the line in active mode (except during the ringburst) is calculated as: ZT ZTR = + 2 (RF + RP) 1000 Thus with ZTR and RF known: ZT = 1000 ˇ (ZTR - 2 ˇ (RF + RP) where ZTR = the SLIC's two-wire (tipring) interface impedance. RF = the line resistor, RP = SLIC protection resistor. ZT = the SLIC twowire impedance programming impedance. Chose RF=40, RP=40. RTR=600 yields RT =442k.
RB = RTX ˇ
ˇ
from which, with our suggested component values, RB=15.8 k
Ring-Signal Connection
The ring-signal can be generated in a CODEC with assistance from the device processor, which may send the appropriate stream of bytes to the CODEC. With this approach any desired ring-signal shape can be generated, maximising output amplitude and minimising EMI. The RSIN and VRX nodes are both connected to the CODEC, and the ring-signal is injected in the same way as an ordinary voice signal. Operation of the Ring Loop During ringing the line voltage is monitored by the differential stage, consisting of an operational amplifier and resistors RDT1, RDR1, RDT2 and RDR2.
where Vg(t) is the signal from the signal source. = RDx1 / RDx2 =1/39, x = TIP / RING. The ring-signal from the SLIC will be balanced about VBat / 2.
The Ring Loop Switch
To connect the ring-loop when ringing there must be an external switch between the RSN input and the RRS and RRG resistor. Normally, when not in ringmode, this switch should be open. This switch could be implemented in different ways, see fig 1. The best performance is achieved using an
6-7
PBL 3860A/6
analogue multiplexer like the 74HC4053 or similar, this device includes three switches. The second best choice is to use the 4066/-16, this device is suitable for two lines. The 4066/-16 device needs a level shifter since the low state must equal VEE , due to the internal design. The noise from the ring loop and ring signal source will be lower in the case of using the 4053. Since this is a double pole switch the signal will be fed to ground when not in ring mode. Control Inputs To be able to use the SLIC as a ringsignal amplifier it must be put in the active state during the ring-burst and NOT in the ring-mode, this is because the internal output stage has to be used. To be able to switch the ring-loop on and off there is an additional control signal: C0. This signal is connected to the switch described in the previous part. state:
I
Preliminary
Application of VBat The battery should be switched to -80V, to be able to fulfil the Bellcore requirements of min 40Vrms over a 5REN load with a sine wave. The battery switching can be solved in one of two ways, either using switching of a dual VBat supply (of -48V and -80V e.g. ), or by using a programmable DC/DC converter. In order to minimise the power dissipation in the SLIC the maximum VBat current shall be limited to 70mA when using a voltage below -60V. A suggestion of a VBat switch is presented in the figure 5, where VBAT2 > VBAT1 . Ring Trip Detection As the SLIC's internal ring-trip detector can't be used in this application, ring trip must be arranged in another way. In the case of up to 5REN load connected to a short line ( of up to 100 ) the SLIC loop detector can be used to detect off-hook during ringing with the help of one extra resistor and a switch, see fig 2.
RD 10k RDR 39k RD 4053 or 4066/-16 C0
This solution minimises the number of external components. There might be a need for software filtering of the detector signal because it will ripple, but in most cases this will not be necessary. See fig 3 for the behaviour of the states at the DET pin and voltage at the RD pin.
1 0
DET GND
trigger level
VEE
ON hook OFF hook
Fig. 3 Ring-trip detector behaviour.
For other cases and methods, please do not hesitate to contact Ericsson Components for assistance. Over-Voltage Protection When using the SLIC as a ring generator the over-voltage protection ( OVP ) must be carefully considered in order to meet the requirements of the SLIC with the higher than usual voltages supplied to the line. As the line voltage, depending of VBat, can be over 60V a programmable transient voltage suppressor must be used. We recommend Texas Instruments TISP PBL1, TISP61CAP3 or TISP61089 which all can handle 80V. Make sure that VBat is connected to the SLIC and the gate of the OVP in the proper way: The SLIC and the OVP ground should be tied together on the PCB. A capacitor of min 220nF should be connected close to the gate of the OVP, to decouple the VBat voltage when the OVP starts to conduct. This can be done by placing the CBat capacitor close to the gate of the transient protector. The RF resistors limits the transient currents and RP limits the currents to the SLIC while the OVP conducts. RP is very important in this application to prevent the output-stages TIPX and RINGX from being damaged, if the OVP conducts during ringing. Power cross protection is provided by the RF resistors in conjunction with the OVP. For the RF resistors, we recommend Ericsson Components' thickfilm resistors PBR510 12/1 (2ˇ40),
C0
II
C1 0 0 1 0 0 0 0 1
C2 0 1 1 1
Open circuit Active Ringing Stand-by
1 1 0 1
For the different types of switches C0 is configured as follows, se fig. 1: I: applies to 4016 and 4066. 4053 can be used in both modes.
RRS 4053 RSN
(a)
VEE
Fig. 2 Ring trip components.
RRG C0
(a)
RRS 4066 /-16 RSN
The RD resistor is calculated as follows 385 ˇ R D RDR = RD ˇ IL - 375 Where IL is the peak line current threshold when ringing. For a 5REN load and a VBAT2 of -80V, IL is 48mA. This results in a RDR resistor of 10k. This can be achieved because of the change in impedance when the phone goes off-hook. During ringing the impedance is larger than 1,4k, even for 5REN, and when a phone goes off-hook it will decrease to less than 500.
RRG
VCC 100k C0 100k BC557
VEE
(b)
Fig. 1 Ring loop switches.
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Preliminary
which are designed to fail open circuit without catching fire when exposed to electrical overload. Power Dissipation The short circuit SLIC power dissipation PShTot is: PShTot= ILShˇ (Vbat - ILSh ˇ 2 ˇ (RF+RP)) + P3 where VBat is the battery voltage connected to the SLIC at pin VBAt. 2.5 ˇ 1000 ILSh = RDC1 + RDC2 is the constant loop current. P3 is onhook active state power dissipation ( typ 200mW; VBat = -48V ). Note that a short circuited loop is not a normal operational condition. The terminating equipment will add some dc resistance ( 150 to 300 ) even if the wire resistance is close to 0. During ringing the highest power dissipation occurs when the line is 0 and maximum number of bells are connected ( 5REN ). With the suggested values given in this note the maximum line current ILmax will be 47 mA. The power drawn from the supply is then with class-B amplifiers: 2 ˇ 80 ˇ 47 PS = + Pidle 2.6W and the CGO capacitor must be short and wide. The SLIC and the OVP ground should be tied together on the PCB. Ring Voltage First we define: Crest factor ^ =
PBL 3860A/6
In this application note we have used an Wien bridge sine wave oscillator. The circuit uses two resistors and one diode to stabilise the amplitude, se fig 4.
VCC 8.2k
V
^
Vrms The following two tables define the voltage over the bell under different conditions. First the load voltage as a function of line length, number of bells and shape of the ring signal when VBat = -80V, RSIN = 2.0V peak. Load #REN RL 1 3 5 1 3 5 1 3 5 0 100 100 0 100 100 0 100 100 Crest factor 1.41; sin 1.41; sin 1.41; sin 1.20 1.20 1.20 1.05 1.05 1.05 Load voltage 52.2 47.2 43.5 62.9 57.0 52.6 72.0 65.2 60.2
1N4004 10k 20k
1.3k
RSIN 360k R C 22nF 360k R 22nF C
Fig. 4 Wien bridge sine wave oscillator.
With components values shown, the RSIN output will be an 1.4Vrms sine wave with a frequency of 20Hz. The frequency is determined by Resistor R and capacitor C according to 1 f= 2ˇRˇC
In the next table the required VBat to achieve a specific voltage over the bell ( 40 or 50 V ) is presented, the load is fixed at 3 or 5REN with 100 wire resistance. RSIN as above. Load voltage 40 40 50 40 50 Crest factor 1.41; sin 1.20 1.20 1.05 1.05 Vbat [V] 3REN 5REN 67.2 56.4 70.5 49.4 61.3 73.0 61.2 76.1 53.2 66.8
The output power from the SLIC is: Pout = Ilrms2 ˇ (Z bell+2 ˇ (RF+RP)) 1.7W This means that the power dissipation in the SLIC is about 0.9W during ringing, which is within the limit for maximum ratings. Unused Inputs / Outputs DT (pin 3), DR (pin 4) and RINGRLY (pin 9) are not used in this application: leave open. PCB Layout Care in PCB layout is essential for proper PBL3860A/6 function. The components connected to the RSN input (pin 16 for PLCC) should be in close proximity to that pin such that no noise is injected into the RSN terminal. Ground plane surrounding the RSN pin is advisable. The track between the gate of the OVP
There is no need to use one oscillator for each line, depending on the amplifiers current capability. So if the current driving capability of the amplifier is high enough, only one oscillator is required per line card, regardless of the number of lines.
Ring Signal Generator There are different ways of generating the low voltage ring signal. One is to use the CODEC as a oscillator, this can be done if access to the PCM bus is provided. The micro controller feeds the CODEC with a stream of bytes to generate the desired frequency and amplitude. Another choice is to use a D/A converter connected to the micro controller. Then there are different kinds of oscillator circuits. 6-9
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